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lexer.go
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lexer.go
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// Copyright 2020 Pokémon GO Nancy
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
//go:generate mockgen -destination ../command/lexer_mock_test.go -package command . Lexer
package command
import (
"io"
"strings"
"unicode"
)
// Lexer tokenizes commands
type Lexer interface {
// HasNext returns true while the lexer has more token to read.
HasNext() bool
// Next returns the next token as string
Next() (string, error)
}
// lexer is an implementation of `Lexer`
type lexer struct {
// command holds the command to tokenize
command []rune
// cursor holds the cursor position
cursor int
// length holds the command length
length int
}
func (l *lexer) min(a, b int) int {
if a < b {
return a
}
return b
}
func (l *lexer) advanceCursor() {
l.cursor = l.min(l.cursor+1, l.length)
}
func (l *lexer) HasNext() bool {
return l.cursor < l.length
}
func (l *lexer) Next() (string, error) {
sb := strings.Builder{}
for l.HasNext() {
current := l.command[l.cursor]
l.advanceCursor()
if unicode.IsSpace(current) {
break
}
sb.WriteRune(current)
}
if sb.Len() == 0 {
if l.HasNext() {
return l.Next()
}
return "", io.EOF
}
return sb.String(), nil
}